For several decades surgical power tools have supported surgeons in their work. As examples of surgical power tools, electric-motor-driven surgical drills, bone saws and screwdrivers for bone screws may be mentioned.
Every surgical power tool includes an operating unit, for example, a movable switch or rotary knob for controlling certain functionalities of the tool. In the simplest case the operating unit may have a tumbler switch for selectively switching the power tool on and off. Multi-stage switches are frequently used, so that a user of the power tool can select between various operating modes. For adjusting a speed of the power tool, rotary operating units such as stepless rotary knobs are coming into use.
Conventional mechanical operating units, such as tumbler switches or rotary knobs, are frequently unsuitable for surgical power tools, and are certainly unsuitable if the tools must be sterilised. This is related to the fact that such operating units include a large number of mechanical moving components which are very difficult to seal to prevent ingress of liquid or gaseous sterilisation media. Ingress of a sterilisation medium into such operating units is detrimental to their operability. For this reason surgical power tools having tumbler switches, rotary knobs or similar mechanical operating units either cannot be sterilised at all or must be serviced after a few sterilisation cycles.
To improve the sterilisability of surgical power tools, or to make it possible in the first place, the mechanical operating units of such tools are frequently replaced by a combination of a force sensor and a signal processing circuit for the force sensor. Force sensors generally have a planar form and have no moving mechanical elements. For this reason force sensors can be installed in a simple and sealed manner below a flexible housing section of a surgical power tool.
Surgical power tools having a force sensor arranged below a flexible housing section are known, for example, from U.S. Pat. No. 3,463,990 and U.S. Pat. No. 6,037,724. In the case of such surgical power tools the force sensor is usually housed within a casing of plastics material which protects the force sensor (and often the associated signal processing circuit also) against a sterilisation medium. It has been found in practice, however, that despite this casing maintenance or exchange of the sensor-based operating units is necessary after only a few sterilisation cycles.
It is an object of the invention to specify an operating unit for a surgical power tool which withstands a large number of sterilisation cycles. It is further an object of the invention to provide a surgical power tool which is better able to be sterilised. A further object of the invention is to specify a calibration method for the power tool.